Cathode-ray tube



Jul 19, 1938. w, HEWNN 2,124,401

CATHODE RAY TUB-E Filed May 11, 1955 Fig. I

Inventor: Walter Heimann,

Patented July 19, 1938 CATHODE-RAY TUBE Walter Heimann, "BerlinReinickendorf, Ger.-

many, assig nor to. General Electric Company, a corporation of New YorkApplication May 11, 1933,.Serial No. 670,551

I In

The present invention .relates to. cathode-ray tubes provided with anelectrostatic control member and used in :theinvestigation of electricor magnetic phenomena.

In tubes of this sort, the electrons emitted by the cathode andaccelerated by :the .anode are causedto. be focused on afiuorescentscreen by means of an electrostatic member whichis sometimes known as..aWehnelt cylinder". In

lan order to increase the concentration .ofthe electrons, there. may beprovided .an inert gas within the envelope, asis well known. The cathoderays. are usually deflected: across. the:v screenby means of a pair .orpairs f plates. to which; the

.15 voltage. under investigationis applied.

It has been found that when the voltage-ape plied. .to the deflecting.plates is less :thanablout 100,000 cycles vper second,- thecombinedeffect of thefocusing member and the gas is usuallysuiificient toproduce a sharpandiwell-defined light spoton the screen. However, at:the higher frequencies, i. e. above 100,000 cycles. per -::second,the'light image becomes fuzzy with an indefinite outline. In order toimprove the light char- 5 acter of the spot at these higher frequencies,the use of a gas of very low atomic weight has been proposed, forexample hydrogen, which tends to constrain the electrons to a beam ofuniform density in cross section. Notwithstand- I 30 ing the improvementin the focusing effect obtained by the use of such a gas, it has stillbeen found that the light spot does not present a clearly defined'imagewhen the cathode-ray beam is deflected at frequencies above the order of35 100,000 cycles per second.

An object of the present invention is to improve the light image whenthe tube is used under high frequency conditions. It has been found thatthe indefinite character of the light 40 image is due in a large degreeto the deleterious electrostatic effects produced on the control memberand having their origin in the deflecting plates. In accordance with myinvention, I propose to electrostatically shield the focusing mem- 45ber from these effects and for this purpose,

provide a metal enclosure which completely surrounds the member. Theinvention will be more 1 fully understood when reference is made to thefollowing specification and accompanying draw- 50 ing in which Fig. 1represents an elevational view, partly broken away and in section, of acathode-ray tube improved in accordance with my invention. Fig. 2 is anenlarged view, in cross section, of an exemplary form of cathode 55which may be used in the tube.

end of the envelope is coated onthe interior carrying a metal cup member5..

Germany May 30,1932 3Claims. (o1. sac-27.5w

. Referring to Fig. 1, numeral 1 designates-the envelope of acathode-ray tube which is pro.- vided with .the usual flared-out portionterminated bya spherical glass wall. The spherical with .a well-knownsubstance which fluoresces whenlstruck by electrons. The other .end' ofthe envelope terminates in a reentrant stem 2 which supports the entireelectrode structure except the deflecting: plates. The cathode, as shownn more clearly in Fig. 2, is. constituted. of a metal cylinder providedat the upper end (as shown) with a transversely extending metal plate 4The interior of the cup may be coated with an electronically activematerial. ,At the extreme upper; end of the cylinder there is a metalcap 6 provided-at :the center with an. electricdischarge opening 1.

Within the cylinder 3., there is a helical form. of

heater fl secured at the upper end to the trans.- .verse disk 4.Leading-in conductors which also serve. the purpose of supportingthecathode structure-are taken, respectively from the lower end of theheater and from the cylinder 3,

through the stem 2 to the exterior.

The anode may take the form of a metal plate 9 having a centraldischarge opening Hi. In order to focus or otherwise control theelectrons passing between the cathode 3 and the anode 9, there may beprovided a cylindrical focusing member ll, mounted in line with theopenings I and In, as shown. The member ll conveniently may be supportedfrom the stem 2 by means of a rigid leading-in conductor I2.

In addition to this electrode structure, the envelope I also containstwo pairs of deflecting plates l3, l4, rigidly mounted in the envelopeby means of stiff wires which extend transversely across the envelope.The respective pairs of plates arearranged in different transverseplanes with respect to the envelope and with respect to one another.

The envelope may contain an inert gas such as argon at a relatively lowpressure.

When a tube of this sort is operated under conditions of high frequency,i. e. when high frequency voltage undulations are applied to thedeflection plates I3, I 4, it has been found that notwithstanding thepresence of a gas within the tube and the focusing cylinder ll chargedto a proper potential for focusing, the light spot on the fluorescentscreen I5 becomes blurred or fuzzy.

In order to reduce this effect, and in accordance with my invention, Iprovide an electrostatic shield I6 about the focusing member I I. Thisshield conveniently may take the form of a metal cylinder secureddirectly to the anode, hence maintained at anode potential, and thebottom of which is completely closed except for a small dischargeopening I! in line with the opening in the cathode. The electrostaticcontrol member II is thus surrounded on allsides by the metal memberexcept for a discharge opening at the top and the bottom of the memberthrough which electrons pass on their way to the screen.

It is evident that while I have shown the member l6 as being made ofsolid metal, this member may take the form of a metal cage or meshenclosure, since its function is solely that of providing a positivefield about the member II which serves to shield the member from thehigh frequency oscillations applied to the deflecting plates I3, M. Itis also apparent that the positive field as exerted by themetalenclosure [6 incidentally functions to accelerate the electronsbetween the cathode 3 and the control member I I. The enclosure Hi canconveniently serve as a support for the anode 9 and for this purpose,there may be provided a rigid leading-in conductor l8 sealed in thereentrant stem 2 and secured to the bottom member of the enclosure.

While I have shown the metal enclosure l6 as being secured directly tothe anode, hence maintained at anode potential, it is evident that theenclosure may be mounted separate from the anode and charged to anysuitable positive potential.

It has been found in accordance with my invention, that when thefocusing member H is completely surrounded by a positively charged metalmember, the electric fields produced at the deflecting plates l3, I4have substantially no effect on the action of the focusing member andhence, the latter is free to exercise its focusing or other controllingeflect on the electron stream as it passes through the anode and betweenthe deflecting plates on its way to the fluorescent screen. By the useof the improved shielding member IS, the light spot on the screen issharply defined, even when the electron beam is deflected at a rapidrate by voltages having frequencies, as high as 200,000 cycles persecond or over, applied to the plates I3, M. I

While I have described my invention in connection with a cathode-raytube of the gaseous type, it is to be understood that the positivelycharged shield I6 also ofiers an advantage by way of increasing theelectrostatic controlling effect of the member H in a highly evacuatedtubecontaining no gas.

What I claim as new and desire to secure by Letters' Patent in theUnited States is:

1-. A cathode-ray tube comprising an envelope containing a cathode, anelectrostatic control member and electron-deflecting plates, and meansfor electrostatically screening said control member from the. deflectingplates, said means including a cylinder completely enclosing said memberexcept for discharge openings and adapted to be'maintained at a positivepotential with respect to the cathode;

2. A cathode-ray tube comprising an envelope containing inert gas, acathode, an electronfocusing member and electron-deflecting plates, andmeans for electrostatically. screening the focusing. member from thedeflecting plates, said means including a cylinder adapted to bemaintained at a positive potential with respect to the cathode andcompletely enclosing solely the electron-focusing member except fordischarge openmgs.

3. A cathode-ray tube comprising an envelope containing gas, a cathode,an anode, an electronfocusing member and electron-deflecting plates,

said anode comprising a cylinder completely closed by a metal wallexcept for discharge openings and enclosing the focusing member.

WALTER HEIMANN.

